Troy Bilt with Pedal Drive/Vari Drive Setup (Best Way to Speed Up?)

I"ve got a 2002 Troy Bilt Lawn Tractor, that features the vari drive system, but is also a pedal drive. From what I understand, swapping the Transmission Pulley to a smaller size, will not help in speeding up the mower, due to the fact that the variable speed pulley controls the mower speed, and the transmission pulley is primarily used for forward/reverse. This thing has a crazy belt size, the upper drive belt on the transmission pulley is like 5/8" x 41.5".....while the lower drive belt is like 5/8" x 90.5." I"ll include a link at the bottom showing how tension on the lower belt is what primarily drives the mower.....My question....... would doing an engine pulley swap really help in speeding up the mower any at all, without trying to modify the trans anyway? Reason I ask, I'm hesitant about trying to mess with this variable speed pulley in any form, since a replacement is like $100 everywhere I look. In addition, changing belt sizes worries me, since the variable speed pulley is basically a double pulley in a sense. I appreciate any help, and I'm not looking to really change the trans at this time. Here is a link I found on Youtube showing how this system operates, thanks: